1. Field of the Invention
The present invention relates to a polymer compound and an organic light-emitting device (OLED) using the same, and more particularly, to a polymer compound which can be used for a hole injection layer and/or a hole transport layer and an organic light-emitting device (OLED) using the same.
2. Description of the Related Art
Luminescent display devices are self-emissive and known for their high visibility, excellent contrast and quick response time. Organic electroluminescent (EL) devices can be classified into inorganic EL devices using inorganic compounds for emissive layers, and organic EL devices using organic compounds for emissive layers. Research into organic EL devices has been increasing, since organic EL devices are known for their excellent luminance, low driving voltage, and fast response time, and are capable of forming multi-color images compared to inorganic EL devices.
For example, according to research conducted by Kodak Corporation in 1987 (Appl. Phys. Lett. 51, 913 (1987)), a separated-function type organic light-emitting device (OLED) having a bilayer structure emits light at an intensity of about 1,000 cd/m2 at about 10 V of applied voltage by using ITO for an anode, Mg—Ag alloy for an cathode, tris(8-quinolinorate)aluminium (Alq3) for an electron-transporting material and an emissive material, triphenyl amine derivatives for a hole-transporting material. This OLED has a stacked structure of electron transport materials and hole transport materials and has an improved emitting property compared to a traditional single-layer type device.
In terms of material properties and manufacturing process, organic light-emitting display devices can be classified into devices using small-molecular materials and devices using polymer materials. Devices using small-molecular materials are manufactured by forming thin layers using vacuum deposition. In manufacturing devices using small-molecular materials, refinement and high purification of light-emitting materials and accomplishment of color pixels are easy. However, there are still problems such as crystallization in thin layers, and lower than desired quantum efficiency, thermostability, and color purity.
Research into OLEDs using polymer materials has proliferated since it was revealed that light is emitted when electricity is applied to poly(1,4-phenylenevinylene) (PPV) of π-conjugated polymer. π-conjugated polymers have an alternating chemical structure of single bonds (or σ-bond) and double bonds (or π-bond) and thus have π-electrons which are allowed to move quite freely and are evenly distributed within the bond chain. Due to such semi-conductive properties of π-conjugated polymers, π-conjugated polymers can be applied in emissive layers of organic light-emitting devices to emit light corresponding to the band gap between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) throughout the whole visible-light region using molecular design. Another advantage of OLEDs using polymers is that thin layers can simply be formed using a spin coating or printing method, and thus the manufacturing process is simplified and costs are reduced. In addition, polymers have a high glass transfer temperature and thus can be used to manufacture thin layers having superior mechanical features.
Thus, research into the application of polymer compounds to organic layers such as a hole injection layer, a hole transport layer, and an emissive layer of OLEDs is ongoing.
It is disclosed in the paper [Advanced materials 2005, 17(8), 1018] that a PEDOT/PSS (polyethylenedioxythiophen/polystylenesulfonate) can be used for hole injection layers of OLEDs, however, it is difficult to coat a large area and to form thick layers using PEDOT/PSS. Besides, when OLEDs are manufactured using vacuum deposition, moisture may be contained in the manufactured devices, which is undesirable for a practical process. In addition, fluoric-containing hydroPEDOT/PSS are unsuitable for forming evenly stacked layers due to the strong surface repulsion force of fluorine in the upper layer.